The present invention relates to a method and a device for installing belts on belt drives, particularly V-belts for driving auxiliary equipment on internal combustion engines. It is known that belt drives that use belts made of elastic material (flat belts, V-belts, serrated belts, etc.) are liable to sag (become elongated) after a period of use following initial installation. As a result, the initially adjusted tension quickly diminishes, and if the belt is not retensioned early on, slipping will occur. It is not possible to compensate for the resulting "sagging" of the belt by increasing initial tension during initial installation, since this produces over-straining in the entire belt drive and belt noise. A prior art solution involves subsequent tensioning of the belt after an initial period of use. However, this is too cumbersome and often involves substantial extra work (i.e. dismantling of beltcover, etc.). For internal combustion engines in automobiles with belt drives that, e.g., drive a generator, early retensioning defeats efforts aimed at ensuring long intervals between maintenance services.